An insulation composite for attenuating energy or sound transmission has a body layer of insulating material with a roughly textured face and a uniform thickness solid cover layer permanently embedded in the body layer to a partial depth so that material of the body layer does not protrude through the surface of the cover layer. The body layer can be rigid board or resilient batting such as fiberglass. The cover layer is formed from a curable fluid cast onto the upwardly facing surface of the body layer. The uniform thickness of the cover layer is achieved by spreading the fluid over the surface utilizing a coating bar having a downwardly facing corrugated profile defining ridges in contact with the body layer and grooves between the ridges, such as a wire wound coating bar Some of the fluid is pressed into the body layer by the ridges while other fluid passes through the grooves then settles to uniform thickness over the wet surface of the body layer. The fluid is then cured to a solid state to form the cover layer.